Preheat the oven to 350 degrees Fahrenheit and either grease a sheet pan or line it with parchment paper.
Clean and destem 24 ounces white button mushrooms, discarding the stems or reserving them for a separate recipe. Place the mushrooms bottom up on the sheet pan.
Add 1 tablespoon unsalted butter to a small skillet and melt over medium heat. Add ¼ cup minced shallot and 1 tablespoon minced garlic and cook for 1-2 minutes, until the shallots pale in color. Remove the shallot mixture from the heat and set aside in a small bowl.
Add 8 ounces cream cheese to a large bowl and beat with a hand mixer until smooth.
Add 1 egg yolk, 1 tablespoon minced fresh parsley, ½ teaspoon paprika, and ¼ teaspoon salt and beat until combined.
Add 12 ounces drained canned crab meat1 cup grated parmesan, and shallot mixture and mix until combined. At this stage, it will become very soft and wet.
Stir in 1 cup plain panko bread crumbs before transferring the crab mixture to a large ziplock bag and snip off the end of it.
Squeeze the crab mixture into the centers of the mushrooms, letting it mound on top.
Bake for 25 minutes or so, until the tops begin to brown. Serve warm.